GnRH secretion is critical for normal human reproduction and defects in GnRH/LH pulses and the preovulatory GnRH/LH surge contribute to many common reproductive pathologies, including amenorrhea, polycystic ovarian syndrome (PCOS), and infertility associated with anorexia nervosa. Despite the long-standing recognition of the importance and functions of the GnRH neuroendocrine system, a detailed knowledge of the pathways by which endogenous gonadal steroid hormones are conveyed to GnRH neurons and control their secretory activity during the ovarian cycle remains elusive. Understanding of the neural substrates responsible for GnRH secretion has been revolutionized in the last few years by identification of the key role of a neuronal subpopulation in the arcuate nucleus that co-expresses kisspeptin, neurokinin B (NKB) and dynorphin (termed KNDy neurons). Genetic mutations in two of the three KNDy peptides, kisspeptin and NKB, lead to human infertility, and there is strong evidence that the third peptide conveys the inhibitory influence of progesterone on GnRH neurons. A number of features of the KNDy neurons suggest that they may play a key role in episodic GnRH secretion, but this hypothesis and the precise role of each of the KNDy peptides remains to be tested. In the current proposal, we will use a combination of physiological, pharmacological, molecular and neuroanatomical approaches to address this and other questions. First, we will determine if the KNDy cell network is critical for episodic GnRH secretion, examining the effects of disrupting each of the KNDy peptides on GnRH pulse shape. Second, we will address the gap in knowledge concerning the normal physiological role of NKB by determining its role in steroid feedback control of GnRH/LH pulses and the GnRH/LH surge. Finally, we will address key unresolved questions about the anatomy of KNDy cells, including the presence of direct synaptic connections between KNDy and GnRH neurons, and the possibility of synaptic plasticity in these connections during the normal estrous cycle. These questions will be addressed using the female sheep, a model that possesses several unique advantages including the ability to directly monitor GnRH in hypophysial portal blood in awake, unanesthesized animals, and an estrous cycle whose neuroendocrine control closely resembles that of the human menstrual cycle. The proposed studies will provide new information on the mechanisms underlying GnRH secretion and the role of NKB that may lay the foundation for the development of better treatments for pathological disruptions of reproductive function, and the design of novel contraceptive techniques